In the field of medicine, it is common to perform a visual examination to diagnose a disease. For example, visual examination of the cervix can be used to identify regions with a high likelihood of abnormal pathology. An important requirement to be able to visually identify abnormal tissue in a region is the ability to accurately and rapidly focus an imaging device (such as an imaging system or optical instrument) accurately on the region. To focus an imaging device, the region of interest must be the correct distance from the imager's “focal point”. Although several methods have been developed for accurate and rapid focusing, they generally rely on multiple light beams or complicated image processing algorithms. The present invention is a simple focusing process that does not use multiple light beams. It addresses the shortcomings of current methods by improving the accuracy, speed, and robustness of focusing methods used in imaging systems or optical instruments.
The following patents and patent applications may be considered relevant to the field of the invention:
U.S. Pat. No. 4,065,778 to Harvey, incorporated herein by reference, discloses an automatic rangefinder and focusing apparatus is provided for use with a camera for determining the distance from an object to be photographed to the film plane of the camera and for positioning the camera's objective lens to focus an image of the object in the film plane.
U.S. Pat. No. 4,494,868 to Lambeth, incorporated herein by reference, discloses an improved automatic rangefinder device having means for projecting a beam of light to illuminate a spot on a distant object, and an image sensor for viewing the object and determining the distance thereto by the observed position of the illuminated spot is disclosed.
U.S. Pat. No. 5,061,062 to Schneiter, incorporated herein by reference, discloses a focus spot controller for a variable depth triangulation ranging system, the ranging system including apparatus for emitting a light bean to be focused onto an object, light sensitive apparatus, lens apparatus for imaging reflected light onto the light sensitive apparatus, and apparatus for calculating system geometry and range from signals received from the light sensitive apparatus.
U.S. Pat. No. 6,277,067 to Blair, incorporated herein by reference, discloses a focusing method of overlapping two laser beams at the focal point of a portable hand-held colposcope.
U.S. Pat. No. 7,253,384 to Barnes et al., incorporated herein by reference, discloses an apparatus comprising of a movable optical element having an optical axis and including one or more focusing elements, and image sensor position along the optical axis, and a radiation source attached to the movable optical element. The radiation source directs a beam onto the sensor at a selected angle relative to the optical axis. It also discloses a process that includes positioning a sensor along an optical axis of a movable optical element, projecting radiation beam at a selected angle onto the sensor from a radiation source attached to the movable optical element and adjusting the position of the movable optical element until the position where the radiation beam falls on eh sensor corresponds to the position where the radiation beam is expected to fall on the sensor when the movable optical element is in focus.
U.S. Patent Application Publication No. 2004/0206882 to Banks et al., incorporated herein by reference, discloses a method and apparatus for evaluating image focus that includes a focusing method that uses four light spots that are projected and aligned with four focusing elements. The invention also discloses automatic adjustment of the image focus.
U.S. Patent Application Publication No. 2003/0184856 to Otaki, incorporated herein by reference, discloses a focus point detection device comprises an illuminator that illuminates a specimen obliquely by letting a light flux at an angle to an optical axis of an objective lens enter in such a way that the optical axis and the light flux cross each other in the vicinity of a point in focus at an object side of the objective lens, an image-forming device that forms an image of the observation plane by converging a light from the observation plane of the specimen via the objective lens and a light amount detector that detects amount of light in response to the image formed by the image-forming device with a light sensor, wherein the light amount detector detects a light other than a regular reflection light from a surface of the specimen. Also, a fluorescence microscope comprises the focus point detection device and the infinity objective lens.